Condor 83:34Al Q The Cooper OrnithologicalSociety 1981

PLOT SIZE AS A FACTOR IN WINTER -POPULATION STUDIES

R. TODD ENGSTROM AND FRANCES C. JAMES

ABSTRACT.-The influence of plot size on the results of a Winter Bird-Pop- ulation Study was explored by dividing a 58.3-ha (144-acre) area of apparently homogeneous mature pine habitat into nine 6.5-ha subplots. Bird density and richness were estimated for the nine subplots. To simulate progres- sively larger sample areas, all possible combinations of the subplot survey results were made. Variation in estimates of the density and species richness in the 6.5-ha subplots was large and it decreased as plot size increased. Most of the variation in the distribution of among subplots was related to variation in the habitat. In addition to the effects of plot size on census results, the choice of an appropriate size involves consideration of factors such as grid size, sampling speed and time available for censusing. The optimal size in this open pine habitat was between 20 and 25 ha. Plots of this size can be surveyed easily in the early morning hours and would provide estimates of approximately 80% of the species seen on a plot three times as large. In the present study, plots of 6.5 ha provided estimates of only 40% (range 16% to 60%) of the species observed on 58.3 ha. Rarefaction, a statistical technique, is applied here as a method of compar- ing species richness among plots of different size. If one standardizes the number of individuals to the lowest number in a set of plots to be compared, rarefaction can be used to determine the number of species expected in a sample of that size.

Avian ecology relies largely on censusing of their effects usually is unknown. Species/ techniques for estimates of community com- area effects are another source of variation position and relative abundance of species. that deserves attention. The number of The standard techniques that are in regular species tends to increase as sampling area use have specific advantages and disadvan- increases. This may be attributable to the tages depending on the objectives of the heterogeneity of the habitat or to the effects study (Jarvinen et al. 1977, Robbins 1978a). of sampling (Connor and McCoy 1979): For regional surveys one might choose the Some studies have been based on com- point count (Jarvinen 1978), frequency sam- parisons among censuses taken on areas of pling (Blonde1 1975), the transect method different size without standardizing them to (Emlen 1977), or the breeding bird survey areas of equal size; others compare cer#sus- (Robbins 1978a). If the objective is to obtain es taken on areas that are too small to sup- detailed quantitative information about the port an adequate representation of the avifauna in a specific habitat, spot-mapping species of birds present. Recommendations on repeated visits probably gives the most for the size of a study area are available: 8- accurate results (Svensson and Williamson 10 ha in wooded habitats (Anon. 1947, Kolb 1969, Robbins 1978a). But even with this 1965, Webster 1966, International Bird intensive method, censuses of breeding Censusing Committee 1970), and 40-100 ha birds (Williams 1936) and wintering popu- in open habitats (IBCC 1970). Most authors lations (Anon. 1947, 1950) as published in agree that, to obtain comparable accuracy, American Birds and elsewhere are subject winter plots should be larger than breeding to sources of error that are difficult to eval- season plots in similar habitats. None of uate. Differences among observers (Enemar these references presents evidence on how et al. 1978), time of day (Robbins 1972, much variation in population estimates is Shields 1977), and season of the year (Jar- attributable to the size of the study plot. vinen et al. 1977) are recognized as possible We report here the results of a Winter biases (Berthold 1976), but the magnitude Bird-Population Study (WBPS) made in an

1341 INFLUENCE OF PLOT SIZE 35

FIGURE 1. The study site is a mature longleaf pine stand near Thomasville, Georgia, having an apparently uniform vegetation stucture. open mature longleaf pine (Pinus palustris) A 58.3-ha (144-acre) square area was divided using forest in southern Georgia in January and a compass and tape measure into nine 6.5-ha (16 acre) subunits. The bird survey was conducted following the February, 1979. We marked the area so that methods described in Audubon Field Notes (Anon. subsamples and combinations of subsam- 1947), Kolh (1965), Robbins (1972) and the IBCC ples could be considered as independent (1970). The results are presented as a WBPS in Amer- surveys for predicting the larger community ican Birds (Engstrom 1980). of birds. The results are used to discuss fac- The size of 6.5 ha for the subplots was selected be- cause it is similar to the 6.1-ha (15 acre) minimum sug- tors involved in the choice of plot size in a gested in Americun Birds for both breeding hird cen- bird survey. suses and winter bird-population studies. The results for these smaller areas were compared and then com- METHODS bined to s emulate’ the results of censuses on succes- sively larger plots. The survey route followed an S- The study site is 2 mi south of Thomasville, Thomas shaped pattern along a grid in which the lines were County, Georgia, on Arcadia Plantation. It is one of the 128 m apart. Care was taken to record hirds crossing few remaining tracts of fully mature longleaf pine in subplot boundaries to minimize duplication. All parts the southeastern United States (Fig. 1). The natural of a subplot were within 64 m of the survey route. occurrence of fire kept large areas of northern Florida There are no special recommendations for the distance and southern Georgia in this type of vegetation in pre- between grid lines for the route in winter bird-popu- historic times (Komarek 1968). This site is now main- lation studies, but the IBCC (1970) recommended 200 tained as a natural area by the Tall Timbers Research m for prairie and tundra and 50 m for closed forest Station and ls burned annually. habitats in the breeding season. C. Rohbins (pers. The forest is composed mostly of trees that are 200, comm.) recommends that the distance between lines and some possibly 300, years old. A narrow strip of should be less in winter studies than in the breeding little-leaf titi (Cyril/a paroifolia) with some sweetgum season because birds of many species are less easily (Liquidambar styraci~ua) and swamp tupelo (Nyssu detected in winter. The walk along the route was timed bi,floru) occurs in a wet area in the center of the site. so that each subplot was completed in 56 minutes. This This titi “stringer” and a few patches of winged sumac was approximately 8.6 mm/ha (3.5 min/acre). Robhins (Rhus copallina) and sapling bitternut hickory (Carya (1972) recommended 12.4 min/ha (5 min/acre) in cordi~ormis) constitute the only shrubby areas on the closed forest habitats. site. The major ground cover species are bracken fern All surveys were started within ?4 minutes of sun- (Pteridium nquilinum), wiregrass (Aristidu strictu), rise, and averaged 3 hours and 45 minutes. A complete and runner oak (Quercus pumilo). Clewell (1978) list- survey ofall 58.3 ha took 8 hours on two days. Although ed many of the herbaceous plants. spreading the survey over two days introduced some 36 R. TODD ENGSTROM AND FRANCES C. JAMES

TABLE 1. Survey results for each 6.5-ha subplot. Data are the number of individuals seen on nine surveys.

Subplots

Species F6 D6 B6 B4 D4 F4 FL? D2 B2 Total*

Wood Duck (Aix sponsa) 0 0 0 0 0 0 0 0 2 2 Red-tailed Hawk (Buteo jumuicensis) 0 0 0 0 1 1 1 0 2 Mourning Dove (Zen&u rnacroum) 1 2 0 2 z 0 2 2 7 20 Great Horned Owl (Bubo uirginiunus) 0 0 7 0 0 0 0 0 0 7 Common Flicker (Coluptes auratus) 0 3 3 2 9 0 6 10 4 34 Pileated Woodpecker (Dryocopus pileutus) 2 0 0 1 0 0 0 0 1 4 Red-bellied Woodpecker (Melanerpes curolinus) 5 7 7 5 10 9 17 10 72 Yellow-bellied Sapsucker (Sphyrupicus uurius) 3 3 6 5 3 6 3 z 3 30 Hairy Woodpecker (Picoides uillosus) 0 0 0 0 0 1 0 0 0 1 Downy Woodpecker (P. pubescens) 1 0 0 0 0 1 0 0 1 3 Red-cockaded Woodpecker (P. borealis) 2 15 19 15 20 17 20 16 26 139 Eastern Phoebe (Sayornis phoebe) 0 0 0 0 1 0 0 0 Blue Jay (Cyunocittu cristutu) 0 0 0 3 4 2 4 1 z 1: White-breasted Nuthatch (Sittu curolinensis) 3 7 7 5 17 7 7 9 12 66 Brown-headed Nuthatch (S&u pusillu) 2 14 12 5 7 7 9 10 3 64 House Wren (Troglodytes uedon) 8 5 10 1 11 24 15 9 0 82 Carolina Wren (Thryothorus Zudouiciunus) 3 0 1 0 9 11 7 2 0 33 American Robin (Turdus migrutorius) 3 20 5 16 20 2 1 2 3 72 Eastern Bluebird (Siuliu siulis) 1 6 0 0 1 11 8 0 0 27 Ruby-crowned Kinglet (Regulus culendulu) 0 0 0 0 0 0 1 0 0 1 Loggerhead Shrike (Lanius Zudouiciunus) 0 2 3 1 1 0 1 3 3 13 Solitary Vireo (V. soliturius) 0 3 1 1 2 0 1 0 2 19 Yellow-rumped Warbler (Dendroicu coronutu) 2 0 1 0 0 11 0 0 20 Pine Warbler (D. pinus) 12 15 15 4 ! 9 11 14 16 95 Palm Warbler (D. puZmurum) 4 7 2 4 1 0 3 0 0 21 Common Yellowthroat (Geothlypis t&has) 3 8 9 5 36 17 26 8 0 110 Eastern Meadowlark (SturneZZu magna) 15 1 21 0 2 0 0 3 47 Red-winged Blackbird (Ageluius phoeniceus) 1 : 0 150 1 250 0 45 90 537 Cardinal (Cardinalis cardinalis) 0 0 0 0 5 0 2 0 0 7 American Goldfinch (Carduelis tristis) 0 0 1 1 7 0 0 0 0 9 Rufous-sided‘ Towhee (Pipilo erythrophthulmus) 2 2 6 1 33 13 63 30 0 146 Swamp Sparrow (Melospiza georgiana) 0 0 8 1 0 0 3 0 0 12 SUBPLOT TOTALS Number of individuals on nine trips 73 125 124 249 216 390 222 173 :191 Total # of species (32/58.3 ha) 19 17 20 21 23 18 23 17 17 Average # individuals/trip** 8 14 14 28 24 43 25 19 21 Species for which there was an average of at least one individual per trip, rounded (25/58.3 ha)? 4 11 12 9 15 12 12 11 7

’ ’ This is the number of individuals seen durin nine surveys for the entire 58.3.ha plot. The sum of subplot values sometimes exceeds the grand total because some individuals (52) were observe d crossmg over subplot boundaries and were counted more than once. ** Individuals recorded on all trips divided by nine, rounded to the nearest whole number. t Species for which the number of individuals divided by the number of trips is less than 0.5 are omitted,

variation, it was the only way to cover the entire plot during morning hours. The 58.3-ha plot was complete- RESULTS ly surveyed nine times in January and February, 1979. CENSUS RESULTS The average minimum temperature of census dates was 1.1% and the average maximum was 13.3%. All We found a total of 32 species in nine com- surveys were made by the senior author. plete censuses (Table 1). The number of in- The order in which the subplots were surveyed was dividual birds seen on each subplot varied arranged to eliminate between-subplot variation in de- from an average of 8 per trip to an average tectability with time of day. To reduce the bias caused by changes in bird detectability during the morning, of 43 per trip and the total number of all subplots were sampled the same number of times, species on each subplot varied from 17 to and during the same parts of the morning, but on dif- 23. Data are reported in American Birds in ferent days (see Methods). Friedmans’ non-parametric terms of the average number of individuals rank sums test (Hollander and Wolfe 1973) showed that seen of each species. Because these aver- differences in the number of birds detected at different hours of the morning were statistically significant. The ages are rounded to the nearest whole num- number of birds observed decreased with hour of the ber, all species having an average of 2 0.5 morning. individuals are recorded as having been To assess variation in the structure of the habitat, 45 seen at least once per trip. The number of 0.04-ha (O.l-acre) circular samples were taken, five ran- domly selected on each of the nine subplots according species seen at least once per trip (rounded) to the method recommended by James and Shugart per 6.5-ha subplot varied from 4 to 15, and (1970). 25 species were seen on the entire plot. INFLUENCE OF PLOT SIZE 37

TABLE 2. Quantitative habitat analysis for nine 6.5-ha subplots.

F6 D6 B6 84 D4 F4 F2 D2 B2

Trees 3 inches DBH and over* 90 36 62 60 50 56 62 44 42 Total basal area (ftVacre at breast height) 59.6 65.6 79.6 95.8 49.4 62 58.8 87.4 63.6 Percent longleaf pine 98 95 87 93 96 96 100 100 95 Longleaf pine trees/acre 88 34 54 56 48 62 44 40 relative density (%)** 98 95 87 93 96 100 100 95 relative dominance (%)t 96 91 82 92 99 90 100 100 99 frequency (%)tt 100 100 100 80 100 100 100 100 100 Size class A (3-6” DBH) trees/acre 40 6 12 0 14 16 12 relative density (%) 44 8 19 0 28 29 19 basal area (ftVacre) 6 0.6 1.2 0 1.4 1.6 1.2 relative dominance (%) 10 0.5 2 0 3 3 2 Size class B (6-9”) trees/acre 10 10 6 0 4 12 18 6 relative density (%) 11 13 10 0 8 21 29 14 basal area (ftVacre) 2 2 1.8 0 1.2 3.6 5.4 1.8 relative dominance (%) 5 3 2 0 2 6 9 3 Size class C (9-W) trees/acre 24 12 14 20 16 4 8 12 18 relative density (%) 26 15 22 33 32 7 13 27 43 basal area (fWacre) 19.2 9.6 11.2 16 12.8 3.2 6.4 9.6 7.2 relative dominance (%) 32 8 14 17 26 5 11 11 23 Size class D (15-21”) trees/acre 14 40 24 34 22 12 relative density (%) 15 51 39 57 if ;: 2236 50 29 basal area (ft*/acre) 25.2 72 43.2 61.2 21.6 28.8 39.6 39.4 21.6 relative dominance (%) 42 62 54 64 44 46 67 45 34 Size class E (21-27”) trees/acre 2 10 4 6 4 8 2 6 2 relative density (%) 4 13 7 10 a 14 3 14 5 basal area (ft*/acre) 6.2 31 12.4 18.6 12.4 24.8 6.2 18.6 6.2 relative dominance (%) 10 27 16 19 25 40 11 21 10 Size class F (27-33”) trees/acre 0 0 2 0 0 0 0 4 4 relative density (%) 0 0 3 0 0 0 0 9 9 basal area (ft*/acre) 0 0 9.8 0 0 0 0 19.6 19.6 relative dominance (%) 0 0 12 0 0 0 0 31 31 Canopy cover (%) 35 51 66 62 36 23 52 45 45 Shrub stems (NoJO. acre) 0 10 0 0 2570 0 0 520 210 Ground cover (%) 100 100 100 100 100 100 100 100 100

* Based on 45 0.1.acre circular samples, five per subplot. ** Percent of total number of trees of all species or within all size classes t Percent of total basal area. tt Percent of circles having this species.

Quantitative habitat descriptions for each in bird density. For instance, subplot F6 subplot plus a cumulative description for had the fewest birds and had a low number the entire plot (Table 2) showed larger vari- of large trees and few shrubs. Subplots D4 ations than we expected. This was apparent and F2 had the highest density of birds in in the density of large trees (range in num- the area. Most of the birds were in the titi ber of trees >21 inches TIBET/acre, 2-lo), stringer in D4 and in the Sassafras and the number of shrub stems (range in num- Rhus in F2. Red-winged Blackbirds roosted ber of shrub stems/acre, O-2,570), and the in subplots B4 and F4 and fed together in percent canopy cover (23-66%). A compar- subplot B2 (Table 1). Common Yellow- ison of the habitat data with the bird distri- throats and Rufous-sided Towhees showed bution among the subplots (Tables 1 and 2) high variation in density between subplots, suggests the basis for some of the variation usually occurring in areas where there was 38 R. TODD ENGSTROM AND FRANCES C. JAMES

Sassafras and Rhus (subplots F2 and D2). TABLE 3. The mean, range, and standard deviation The Great Horned Owls in subplot B6 were of the number of individuals and species in all possible combinations (N) of subplots that can be made to form nesting. Four clans of Red-cockaded Wood- different sizes of plots. The estimated number of peckers, each with 4-5 birds inhabited the species seen an average of at least once per trip, E(S), study area and two more clans roosted near- for samples of this number of individuals was deter- by. This is an exceptionally high density, mined by rarefaction. indicating that the area may be optimal hab- itat for the species. Red-cockaded Wood- peckers were occasionally seen in mixed 6.5 ha 9 Ind. 22 843 (16 acres) flocks with Brown-headed and White- Species* 10 4-15 E(S) 11 5.7-15.6 breasted nuthatches, Pine Warblers, and 13 ha 36 Ind. 43 22-71 Solitary Vireos. Cardinals, American Gold- (32 acres) Species 16 12-20 finches, and Swamp Sparrows were all seen E(S) 15.6 11.0-19.0 most often in or near the titi stringer in the 19.4 ha 84 Ind. 65 28-95 center of the plot. The Eastern Meadow- (48 acres) Species 19 15-23 larks occurred in flocks and appeared to E(S) 18.4 12.6-20.9 roost at night beneath the thick carpet of 25.9 ha 126 Ind. 87 55-120 wiregrass. (64 acres) Species 21 18-25 E(S) 20.4 17.3-22.4 ESTIMATES OF THE COMMUNITY BASED ON 32.4 ha 126 Ind. 109 76-141 SAMPLES OF DIFFERENT SIZE (80 acres) Species 23 19-25 The subplot data were treated as nine in- E(S) 21.8 19.5-23.4 dependent 6.5-ha replicates. The results of 38.9 ha 84 Ind. 130 100-160 all possible combinations of the subplot (96 acres) Species 23 20-25 23.0 21.3-24.1 data are summarized in Table 3. Combina- E(S) tions of adjacent subplots were considered 45.3 ha 36 Ind. 152 125-174 (112 acres) Species 24 21-25 but the results were very close to the results E(S) 23.8 22.7-24.5 of all-possible combinations. Birds ob- 51.8 ha 9 Ind. 174 152-189 served crossing over subplot boundaries (128 acres) Species 25 23-25 were subtracted from the combined results. E(S) 24.6 23.8-25.0 The average number of species seen at least 58.3 ha 1 Ind. 189 once per trip based on all possible combi- (144 acres) Species 25 nations of subplots increased from 10 to 25 * Species seen an average of once per trip. as plot size increased from 6.5 to 58.3 hect- ares (Table 3). The range of 11 species (4- 15) in the number of species in the subplots is disturbingly large. The range decreases per census trip on the study area. The rar- regularly with increasing area. The average efaction curve shows the rate of accumula- number of species seen on the nine sub- tion of new species with increasing number plots was 10, which is only 40% of the num- of individuals. The number of species on ber of species seen on the full area. The plots of different sizes was estimated by rar- sample size required to obtain 80% of the efaction, using the number of individuals species on 58.3 ha is between 19.4 ha and from the all-possible combinations data (Ta- 25.9 ha. ble 3). The average number of species and individuals from the all-possible combina- RAREFACTION tions data for each size class are added to Rarefaction is a statistical technique that the rarefaction curve (Fig. 2). The number can be used to generate a curve of the ex- of species determined by all possible com- pected number of species in smaller sam- binations of the 6.5-ha subunits is close to ples of individuals than the original sample the number of species estimated by rarefac- (Sanders 1968, Hurlbert 1971, Fager 1972, tion (Fig. 2 and Table 3). Simberloff 1978). Given N individuals dis- Densities reported in the WBPS are stan- tributed in S species, the expected number dardized to densities expected on 40.5 ha of species [E(S)] and its standard deviation (100 acres) and on 1 km2. To investigate the can be calculated. Heck et al. (1975) used effects of this procedure, we standardized this technique to assess sampling efficiency the density of individuals to 40.5 ha for all by comparing effort with sampling results. of the progressively larger sample areas. We calculated a rarefaction curve (Fig. 2) The estimated number of species, E(S), was for the avian community, using the relative calculated by rarefaction for these standard- abundance of all species seen at least once ized densities (Table 4). Variation in the INFLUENCE OF PLOT SIZE 39

TABLE 4. The number of individuals per trip per 40.5 ha (100 acres) in plot size classes, as determined .*e by all possible combinations (N) of the nine 6.5-ha sub- plot, and the number of species, E(S), estimated by _- ’ / /,,; . , ’ rarefaction corresponding to the estimated number of I , ’ / I ’ individuals. 1 ’ ,/ / ‘ I / ’ Plot size N Range I ’ 1 I ’ 6.5 ha 9 I&40.5 ha 50-269 ; I ’ (16 acres) E(S)/40.5 ha 16.6-* / ’ // 13 ha 36 I&40.5 ha 69-222 ;_I (32 acres) E(S)/40.5 ha 18.8-* 2’0 4’0 60 60 lb0 Ii0 140 160 180 200 19.4 ha 84 I&40.5 ha 75-200 (48 acres) E(S)/40.5 ha 19.1-* NUMBER OF INDIVIDUALS 25.9 ha 126 I&40.5 ha 86-188 FIGURE 2. The rarefaction curve is generated from (64 acres) E(S)/40.5 ha 20.3-25.0 the relative distribution of the total number of individ- uals among the species on the entire 58.3-ha plot. The 32.4 ha 126 I&40.5 ha 95-176 dashed line is two standard deviations from the curve. (80 acres) E(S)/40.5 ha 20.9-24.6 The average number of species and individuals from 38.9 ha 84 I&40.5 ha 104-167 all possible combinations of the 6.5-ha subunits are (96 acres) E(S)/40.5 ha 21.5-24.3 superimposed on the rarefaction curve. Thus the dots from left to right are the average numbers of individ- 45.3 ha 36 I&40.5 ha 111-155 uals and species for the eight area classes shown in (112 acres) E(S)/40.5 ha 21.9-24.1 Table 3. 51.8 ha 9 Ind140.5 ha 119-147 (128 acres) E(SY40.5 ha 22.4-23.6

* The number of individuals estimated by all possible combinations of the data exceeds the number of individuals actually obsewed in the 58.3. number of individuals per 40.5 ha estimated ha plot, so no estimate of the number of species can be made by rarefac- tion. from the subplots was large. This variation decreased as the plot size increased. Rare- faction cannot be used to estimate the num- trees by size class, the percent canopy cov- ber of species found in a sample larger than er, and the distribution of shrubs varied the observed number of individuals. The substantially among the subplots (Table 2). number of individuals standardized to 40.5 Variation in the distribution of the birds ha in the three smallest plot sizes exceeds among subplots appears to be attributable the actual sample found on the 58.3 ha plot, largely to variation in the structure of the so the number of species cannot be esti- habitat. This variation makes us cautious mated for these densities. about interpreting the species richness re- sults of wintering bird population studies DISCUSSION based on small study plots. We think that standardization of methods Extrapolation of densities from small and considerations of species/area effects plots to standards such as the 40.5 ha and 1 should be given more attention in studies km2 as recommended in American Birds involving bird censuses. The classic conclu- magnifies variation in density to an unrea- sion of MacArthur and MacArthur (1961) sonable level. The range in the number of that bird species diversity during the breed- individuals extrapolated to 100 acres from ing season increases with foliage height di- the subplot results is 50-269 (Table 4). Fur- versity was based on comparisons among 2- thermore, there is no way to extrapolate an ha (5-acre) plots. Willson (1974) based her estimated number for species richness. A study of habitat structure on 21 areas vary- better means of comparing the species rich- ing in size from 5 to 25 ha. Cody (1974) ness of bird communities is to standardize based his investigation of community struc- census data to equal numbers of individuals ture on plots varying from 2 to 6 ha. Rare- and to derive an estimated number of faction is the only method we know by species by rarefaction. The number of in- which species richness can be compared dividuals on plots above a minimum size, between plots of different size and density. 10 ha for example, can be corrected to that The apparent uniformity of the habitat in minimum level, and then the number of our study (Fig. 1) was deceptive. This is species can be estimated for the standard consistent with the results of a study of the size. We have examined how bird density species/area relationship by Kilburn (1966) and species richness vary on small plots. in jack pine forests (Pinus banksiana) in the Rarefaction ignores this variability and can midwestern U.S. Our vegetation analysis only supply species richness estimates as if shows that estimates of the density of the the habitat were homogeneous. While this 40 R. TODD ENGSTROM AND FRANCES C. JAMES should be recognized, rarefaction is still LITERATURE CITED preferable to standardizing densities to 40.5 ANON. 1947. Announcement of the Winter Bird-Pop- ha and reporting species richness for a dif- ulation Study. Audubon Field Notes 1: 165-166. ferent sized area. ANON. 1950. Revised instructions to the Winter Bird- Certain general concepts in ecology can Population Study. Audubon Field Notes 4:184- 187. be examined with data generated by the BERTHOLD, P. 1976. Methoden der Bestandserfas- Breeding Bird Censuses and the Winter sung in der Ornithologie: Ubersicht und kritische Bird-Population Studies. To date, remarka- Betrachtung. J. Ornithol. 117:1-69. bly little analysis has been applied to them. BLONDEL, J. 1975. Lanalyse’ des peuplements Udvardy (1957) and Webster (1966) used doiseaux,’ element dun’ diagnostic Ccologique. I: La methode des Echantillonages Frequentiels published BBCs’ and WBPSs’ respectively Progressifs (E.F.P.). Terre Vie 29:533-589. to look at species number and avian density CLEWELL, A. F. 1978. The natural setting and vege- in the eastern and western United States, tation of the Florida panhandle. Report for the U.S. plotting species number against latitude Army Corps of Engineers, Contract no. DACWOl- 77-C-0104, Mobile, AL. and longitude to indicate geographic diver- CODY, M. L. 1974. Competition and structure of bird sity gradients. Lynch and Whitcomb (1977) communities. Monogr. Popul. Biol., Princeton studied population trends of migrant war- Univ. Press, Princeton, NJ. blers occupying the interior of forests using CONNOR, E. F., AND E. D. MCCOY. 1979. The statis- long-term data from American Birds BBCs.’ tics and biology of the species-area relationship. Am. Nat. 113:791-833. They selected eight BBCs’ on plots of 7-32 EMLEN, J. T. 1977. Estimating breeding season bird ha (18-80 acres) in Maryland, Michigan, densities from transect counts. Auk 94:455-468. and Georgia, some having data dating back ENEMAR, A., B. SJOSTRAND, AND S. SVENSSON. 1978. to 1947. Robbins (197813) has used the vege- The effect of observer variability on bird census results obtained by a territory mapping technique. tation data to predict the abundance of par- Ornis. Stand. 9:31-39. ticular bird species in a given forest envi- ENGSTROM, R. T. 1980. Winter bird-population study ronment. No. 15. Am. Birds 34:29-30. The choice of plot size involves a com- FAGER, E. W. 1972. Diversity: a sampling study. Am. promise. Large plots require more time to Nat. 106:293-310. HECK, K. L., JR., G. VAN BELLE, AND D. S. SIMBER- census, yet small plots have more variable LOFF. 1975. Explicit calculation of the rarefaction results. The 58.3 ha plot surveyed in this diversity measurement and the determination of study was chosen for experimental purpos- sufficient sample size. Ecology 56: 1459-1461. es, not as an optimal size. The disadvantage HOLLANDER, M., AND D. A. WOLFE. 1973. Nonpara- metric statistical methods. Wiley and Sons, New of so large a plot is that a full census re- York. quires two mornings to complete. Important HURLBERT, S. H. 1971. The nonconcept of species criteria for the determination of avian cen- diversity: a critique and alternative parameters. sus plot size are (1) use of a grid distance Ecology 52:577-586. that allows good visibility in the habitat, (2) INTERNATIONAL BIRD CENSUS COMMITTEE. 1970. Recommendations for an international standard for ability to complete a census or survey in the a mapping method in bird census work. Audubon early morning, and (3) maximization of plot Field Notes 24:722-726. size so the avifauna is adequately repre- JAILIES, F. C., AND H. H. SHUGART, JR. 1970. A quan- sented. A plot size of 20-25 ha in open pine titative method of habitat description. Am. Birds 241727-736. habitat was necessary to sample 80% of the J.%RVINEN, 0. 1978. Estimating relative densities of species observed on the 58.3-ha plot, We land birds by point counts. Ann. Zool. Fenn. feel that an area of 20-25 ha is a reasonable 15:290-293. size because it provides an adequate sample J;~RVINEN, O., R. A. V&S;~NEN, AND Y. HAILA. 1977. of the avifauna and it can be surveyed easily Bird census results in different years, stages of the breeding season and times of day. Ornis. Fenn. in a morning. In 1979, 20 of 120 WBPSs’ 54: 108-118. published in Americun Birds were con- KILBURN, P. D. 1966. Analysis of the species-area re- ducted on plots smaller than 8 ha (20 acres). lation. Ecology 47:831-843. A plot this small on our study area would KOLB, H. 1965. The Audubon winter bird-population study. Audubon Field Notes 19:432-434. have been insufficient to represent the avi- KOMAREK, E. V. 1968. Lightning and lightning fires fauna of the habitat. as an ecological force. Proc. VII Ann. Tall Timbers Fire Ecol. Conf: 169-197. ACKNOWLEDGMENTS LYNCH, J. F., AND R. F. WHITCOMB. 1977. Effects of the insularization of the eastern deciduous forest We thank J. L. Wade for permission to work on the on avifaunal diversity and turnover, pp. 461-490. Arcadia Plantation. and the Tall Timbers Research Sta- In A. Marmelstein 1Proiect leaderl. Proc. of Na- tion for financial assistance. C. Robbins, D. Simberloff, tional symposium on classification,-inventory and D. Strong, G. Niemi, N. Warner, and D. B. Means made analysis of fish and wildlife habitat. U. S. Dep. helpful comments on various drafts of the manuscript. Inter., Phoenix, AZ. INFLUENCE OF PLOT SIZE 41

MACARTHUR, R. H.,AND J. W. MACARTHUR. 1961. On ment: Quantitative and statistical analyses, ASTM bird species diversity. Ecology 42:594-598. STP 652. American Society for Testing and Ma- ROBBINS, C. S. 1972. An appraisal of the winter bird- terials. population study techniques. Am. Birds 26:688- SVENSSON, S., AND K. WILLIAMSON. 1969. Recom- 692. mendations for an international standard for a ROBBINS, C. S. 1978a. Census techniques for forest mapping method in bird census work. Bird Study birds. In R. M. De Graaf [ed.], Proc. of the work- 16:249-255. shop on management of southern forests for non- UDVARDY, M. D. F. 1957. An evaluation of quantita- game birds. U.S. Dep. Agric. tive studies on birds. Cold Spring Harbor Symp. ROBBINS, C. S. 197813. Determining habitat require- Quant. Biol. 22:301-311. ments of nongame species, pp. 57-68. Trans. 43d WEBSTER, J. D. 1966. An analysis of winter bird-pop- North American wildlife and natural resources ulation studies. Wilson Bull. 78:456-461. conference. WILLIAMS, A. B. 1936. The composition and dynamics SANDERS, H. L. 1968. Marine benthic diversity: a of a beech-maple climax community. Ecol. Mono- comparative study. Am. Nat. 102:243-282. gr. 6:317-408. SHIELDS, W. M. 1977. The effect of time of day on WILLSON, M. F. 1974. Avian community organization avian census results. Auk 94:380-383. and habitat structure. Ecology 55:1017-1029. SIMBERLOFF, D. S. 1978. Use of rarefaction and re- lated methods in ecology, pp. 150-165. In K. L. Depurtment of Biological Science, Florida State Uni- Dickson, John Cairns, Jr., and A. J. Livingston versity, Tallahassee, Florida 32306. Accepted for pub- [eds.] Biological data in water pollution assess- lication 20 May 1980.

Condor83:41 @ The CooperOrnithological Society 1981

RECENT PUBLICATIONS

Papers in Avian Paleontology Honoring Hildegarde shorebirds as recently suggested. Previous anatomical Howard.-Edited by Kenneth E. Campbell, Jr. 1980. information is reviewed and the appendicular myology Contributions in Science No. 330, Natural History Mu- of the Australian Banded Stilt (Cladorhynchus leuco- seum of Los Angeles County. 260 p. Paper cover. cephalus) is described and discussed. Evidence from $20.00 plus $1.25 for handling and postage. Source: osteology, natal down, oology, parasitology, life histo- Bookshop, Museum of Natural History, 900 Exposition ry, and behavior is also considered. A new stilt-like Blvd., Los Angeles, CA 90007. “Nineteen papers in from the early Middle , Juncitarsus avian paleontology-including theoretical aspects, fau- gracillimus, is described and other aspects of paleon- nal studies, reviews of specific groups, the description tology of are discussed. The filter feeding of several new forms, and archaeological studies-” are apparatus of flamingos is shown to be entirely different presented in this festschrift. Preceding these are ap- from that of ducks and strikingly convergent toward preciations of Hildegarde Howard by Theodore that of baleen whales. Putting everything together, the Downs, Jean Delacour, and Herbert Friedmann; the authors conclude that the Phoenicopteridae are char- bibliography of Dr. Howard and an index to avian taxa adriiforms, most closely allied to the Recurvirostridae. that she described. Also included are the famous illus- Their case is carefully built from several directions and trations of avian osteology, drawn by Frieda Aber- it appears to settle the question. Drawings, photo- nathy, from “The Avifauna of the Emeryville Shell- graphs, and references. mound,” one of Howards’ most important papers. The articles themselves have been contributed by most of p resbyornis and the Origin of the Anseriformes todays’ leading paleornithologists, making the volume (Aves: Charadriomorphae).-Storrs L. Olson and a fitting tribute to Dr. Howard and a significant collec- Alan Feduccia. 1980. Smithsonian Contributions to tion for those who study the fossil history of birds. Zoology No. 323, Smithsonian Institution Press, Wash- They are individually furnished with illustrations and ington, D.C. 24 p. Paper cover. The authors discredit references. Included among them is a description, by evidence purportedly allying the Anseriformes with Campbell and E. P. Tonni, of a tremendous new ter- the Galliformes. Instead, from an examination of the atorn from the late Miocene of Argentina. With an es- Eocene fossil Presbyornis, particularly its filter-feed- timated wingspan of 6.5 to 7.5 m, it was the largest ing apparatus, they propose that the Anseriformes flying bird known to science. evolved from the Charadriiformes. Along the way, they show that screamers are hiehlvy , derived anseriforms. suggest that the major subgroups of anatids may need Relationships and Evolution of Flamingos (Aves: rearrangement, and propose a scenario for anseriform Phoenicopteridae).-Storrs L. Olson and Alan Fed- evolution. Their argument appears to rest on a thor- uccia. 1980. Smithsonian Contributions to Zoology NO. ough analysis, so it is likely to be controversial among 316, Smithsonian Institution Press, Washington, D.C. avian systematists and paleontologists. Drawings, pho- 73 p. Paper cover. This technical paper re-examines tographs, and references. the problem of the ancestral relationship of the flamin- gos-whether to storks or ducks as long disputed, or to